Expression and function of RIG-I in oral keratinocytes and fibroblasts.

Background: Innate immune response by oral mucosal cells may be the first line of host defense against viral infection. Retinoic acid-inducible gene-I (RIG-I) recognizes viral dsRNA in the cytoplasm, and RIG-I-mediated signaling regulates antiviral type I IFN, and inflammatory chemokine production. Here, we tested the hypothesis that oral mucosal cell participation in host defense against viral infection via RIG-I.

Methods: RIG-I expression was detected in immortalized oral keratinocytes (RT7), oral fibroblasts (GT1) using and RT-PCR and immunohistochemistry. RT7 and GT1 were exposed to dsRNA virus mimic Poly I:C-LMW/LyoVec (PLV). Expression of IFN-β and CXCL10 via RIG-I was examined by Real-time RT-PCR and ELISA. Phosphorylation of IRF3 and STAT1 were detected by western blotting.

Results: RT7 and GT1 constitutively expressed RIG-I in the cytoplasm. Furthermore, PLV increased IFN-β and CXCL10 productions in both RT7 and GT1 via RIG-I concurrent with phosphorylation of IRF3 and STAT1. PLV-induced CXCL10 production was attenuated by neutralization of IFN-β and blocking of IFN-α/β receptor (IFNAR), indicating primal IFN-β production via the RIG-I-IRF3 axis, which eventually induces CXCL10 production via the IFNAR -STAT1 axis.

Conclusion: We propose that RIG-I in oral keratinocytes and fibroblasts may cumulatively develop host-defense mechanisms against viral infection in oral mucosa.